The objective of this project is to develop a simple, quantitative point-of-care test for heparin, a drug that is used to prevent clotting during most surgical procedures, especially those requiring an extracorporeal loop. As the continued presence of free heparin after surgery is dangerous to the patient, protamine is usually administered to reverse the anticoagulant effect of heparin at the conclusion of surgery. The method most often used for heparin measurement is a non- specific bioassay that measures activated clotting time of a patient's blood. Phase I studies will demonstrate the feasibility of measuring heparin in whole blood samples using protamine titration in a disposable cartridge. The titration end-point is determined by an optical reflectance measurement of a protamine-specific chromoionophore incorporated into a lipophilic polymer cast onto a highly reflective membrane. Heparin is titrated with several cartridges containing varying amounts of protamine which complexes the free heparin of the sample, and the presence of any excess protamine is then measured. In Phase II we will construct a prototype instrument that can automatically perform a protamine titration of heparin in whole blood samples. PROPOSED COMMERCIAL APPLICATION Practical point-of-care instrumentation that could directly monitor heparin levels in whole blood samples from patients would be extremely useful in the management of heparinized patients. Compared to the current bioassay, the proposed optical sensor offers much better specificity, thereby eliminating a large degree of uncertainty in assessing the cause of patient bleeding and consequently the over- prescription of protamine.